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Mast Building Method

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downunder
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Mast Building Method

Postby downunder » Tue Oct 18, 2016 5:28 am

Getting into thinking :)

I did run some samples for my mast with a wood as a core. The carbon between wood strips does make a difference. Which got me thinking how to make a structurally sound and light mast.

I-Beam. How to build an I-Beam. Would this work as building a U-profile in the middle with UNI carbon and I-Beam with 12x2mm carbon rod? Everything would be wrapped into carbon after.

One could "pre sand" a middle piece of wood before glassing all the parts so not end up with much carbon exposed after. Obviously, as a result of this mast would be squarish shape and sanding is needed to a foil profile.
mast.png
Any thoughts?

Thx

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Re: Mast Building Method

Postby Lokihel » Tue Oct 18, 2016 6:04 am

From an engineering point of view, the stiffness of the mast comes from the carbon on the outside.
The further away from the centre you are, the better it is to resist bending.

Adding carbon to the core of your mast will not do that much to add to stiffness. When you consider all the extra work you have to do, it is really not worth it.
Also, your carbon in the core is not properly bonded to the carbon on the outside, so it will not 'work' as a single piece of carbon like your skin, if you did it correctly.

If you want to make a stiffer mast, the best options are:
- make your mast a little thicker. It will not add much drag, but will add a lot of stiffness. Most of your drag comes from the wings because they are generating lift. Your mast isn't.
- invest in high or ultra-high modulus carbon. These things actually exist, but you will also need to cook it in an autoclave with a vacuum bag etc. So the cost is a lot more.

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Re: Mast Building Method

Postby Blackrat » Tue Oct 18, 2016 6:47 am

ditto

also, make sure you use a hydrofoil profile and not a aircraft profile

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Re: Mast Building Method

Postby downunder » Tue Oct 18, 2016 8:47 am

Thanks for your reply.

Loki,

the I-Beam is a Holly Grail of bounding. :)

This is the only I-Beam that I know of on this forum

viewtopic.php?f=199&t=2390517&start=50

viewtopic.php?f=199&t=2390517&start=80

It is almost funny when I check the new TT boards (and the sales person does not know me), they're all into I-Beams :) New tech, our beam is better then theirs :)

When looking at ultra-high modulus carbon one should consider the shear and peel strength of epoxy. There is absolutely no need to use a high modulus when not using adhesive with very high shear and peel strength.

Blackrat,

this is obvious. But highly iterative process. What might work for others might not work for the rest.

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Re: Mast Building Method

Postby Lokihel » Tue Oct 18, 2016 9:01 am

The I-beam only works properly if it one piece.

To get that effect on your mast section you must laminate the skin and 'beams' together, with continuous fibres going through the middle of the section. Something like a figure of eight shape around the wood core.

If you plan on making a reinforced wood/carbon core, than is then laminated with a separate skin, I don't think it will work that well. It certainly won't be worth the effort, because it will only be epoxy holding the stiffened core and the skin together.

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Re: Mast Building Method

Postby evan » Tue Oct 18, 2016 9:53 am

Those beams only help with hollow structurs or when your core is too soft for the forces in the skin. The only purpose of a core is to connect the composite skins in a non compressive way, thats how honeycomb cores do their work.

When you have a good solid wood core or other non compressible material those beams only serve as a marketing tool or when you want a hollow structure.

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Re: Mast Building Method

Postby tahoedirk » Tue Oct 18, 2016 5:23 pm

That flat carbon rod looks way effective to me, but seems like lots of work and might make it difficult to nail the profile. Other than being heavy solid carbon is pretty easy IF you make a mold.

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Re: Mast Building Method

Postby downunder » Thu Oct 20, 2016 3:17 am

Ordered some carbon rods, will know when I build it I guess.

The mold is easy, I have new alu Manta mast I made a mold off. However, I think it is overkill to build a full carbon mast when one can buy alu for $100 or less...
It is all about the trade off's.

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Re: Mast Building Method

Postby revhed » Thu Oct 20, 2016 5:22 pm

downunder wrote: The mold is easy
Would mind sharing in detail how you make your molds please?
R H

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Re: Mast Building Method

Postby plummet » Thu Oct 20, 2016 7:11 pm

Here's my throught.

There is definite structural advantages in am I beam construction technique.

I think there needs to be a wrap on the top skin to get a strong bond on the outer surfaces. In the perfect world there it would be a one piece layup to get a chemical bond with I beam and top skins. But that will be real challenging.

I don't see an advantage in 2 internal layers of carbon running parallel to the outer skins.

Also there could be a case for using pultruded carbon rod for the leading edge.
i beam.jpg


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